The invention relates to an electric motor with permanent magnet excitation.
DE 35 39 851 A1 has disclosed an electric starter motor for an internal combustion engine, said starter motor having permanent magnets on the pole housing which surround an armature shaft with an armature arranged thereon. The permanent magnets are fixed in the housing with the aid of holding springs, which are arranged between adjacent magnets and have spring arms bearing against one end side of the magnets in a resilient manner. In order to achieve a series characteristic, in which high torques are emitted even at low rotation speeds, flux guidance pieces are associated with the permanent magnets, said flux guidance pieces consisting of a material with good magnetic conductivity and serving to guide the magnetic flux. In accordance with DE 35 39 851 A1, the holding springs are additionally fastened on the housing with a rivet in order to be able to absorb the radial forces acting on the flux guidance pieces and to hold the magnets including the flux guidance pieces in the housing in the desired position.
In accordance with a further embodiment described in DE 35 39 851 A1, the permanent magnets including the flux guidance pieces are positioned on the pole housing with the aid of holding rings, which secure the permanent magnets and the flux guidance pieces radially with respect to the surrounding pole housing. Spring tongues which protrude out of the holding rings through 90° place the flux guidance pieces against the magnets in the circumferential direction. Both the holding via riveted-in holding springs and via the holding rings or in the form of welded-in or riveted flux guidance pieces with simple holding springs represent comparatively complex embodiments.